With the development of various portable electronic devices such as mobile phones, PDAs and notebook computers, the demand for a light, thin and small flat panel display device is increasing. Research is actively being conducted for flat panel display devices such as an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display), or the like. Of them, the LCD device receives much attention due to its simple mass-production technique, easy driving system and high picture quality.
The LCD device has various display modes according to the arrangements of liquid crystal molecules. A TN-mode (Twisted Nematic Mode) LCD device has widely been used due to such advantages as high contrast ratio, rapid response time and low driving voltage. In such a TN mode LCD device, when a voltage is applied to liquid crystal molecules horizontally aligned with two substrates, the liquid crystal molecules rotate and then are almost vertically aligned with the two substrates. Accordingly, when a voltage is applied, the viewing angle of the TN mode LCD device becomes narrow due to a refractive anisotropy of the liquid crystal molecules.
To solve such a narrow viewing angle problem, various kinds of modes of the LCD device having a wide viewing angle have recently been proposed. Among them, an IPS-mode (In-Plane Switching Mode) LCD device is being mass-produced. The IPS-mode LCD device aligns liquid crystal molecules on a plane by forming at least a pair of electrodes in parallel with each other in a pixel and then forming a horizontal electric field substantially parallel with the surface of the substrate between the two electrodes.
FIG. 1 illustrates a structure of the above-described IPS-mode LCD device. As shown in FIG. 1, an IPS-mode LCD has a structure that electrodes disposed in one pixel and forming a horizontal electric field are bent. The electrodes are bent to divide a pixel into two domains, thereby improving a viewing angle characteristic.
As shown in FIG. 1, a gate line 3 and a data line 4 disposed vertically and horizontally define a pixel of an liquid crystal panel 1. Although only one pixel, (n, m)th pixel, is illustrated in FIG. 1, the liquid crystal panel 1 has ‘N(>n)’ number of the gate lines 3 and ‘M(>m)’ number of the data lines 4, and thus has ‘N×M’ number of pixels. The data line 4 is bent at a certain angle and symmetrically arranged with respect to the center of the pixel.
A thin film transistor 10 is formed near the crossing of the gate line 3 and the data line 4. The thin film transistor 10 includes: a gate electrode 11 to which a scan signal from the gate line 3 is applied; a semiconductor layer 12 formed on the gate electrode 11 and forming a channel layer, which is activated when the scan signal is applied; a source electrode 13 and a drain electrode 14 formed on the semiconductor layer 12, to which an image signal inputted from the outside is applied through the data line 4.
A common electrode 5 and a pixel electrode 7 formed in a zigzag shape and arranged substantially parallel with the data line 4 are disposed in the pixel. In addition, a common line 16 connected to the common electrode 5 is disposed at an upper part of the pixel, and a pixel electrode line 17 connected to the pixel electrode 7 is disposed on the common line 16 and overlaps the common line 16.
A column spacer 18 for maintaining a uniform cell gap of the liquid crystal panel is formed on the gate line 3 on the left side of the data line 4.
Referring to FIG. 2, the IPS-mode LCD device having such a structure will be described in more detail. As shown in FIG. 2, the gate electrode 11 is formed on a first substrate 20 and a gate insulating layer 22 is formed on the gate electrode 11. The semiconductor layer 12 is formed on the gate insulating layer 22, and the source electrode 13 and the drain electrode 14 are formed on the semiconductor layer 12. A passivation layer 24 is formed over the first substrate 20.
The common electrode 5 is disposed on the first substrate 20 and the pixel electrode 7 is disposed on the gate insulating layer 22, so that a horizontal electric field is generated between the common electrode 5 and the pixel electrode 7.
A black matrix 32 and a color filter layer 34 are formed on a second substrate 30. The black matrix 32 where liquid crystal molecules do not operate is provided to prevent light leakage, and is mainly formed on the thin film transistor 10 region and between the pixels (i.e., regions of gate lines and data lines). The color filter layer 34 including R (Red), B (Blue) and G (Green) color filters is provided to display colors. In addition, the column spacer 18 is formed between the first substrate 20 and the second substrate 30 to maintain a uniform cell gap of the liquid crystal panel 1.
In general, a ball spacer having a ball shape is widely used as a spacer. The ball spacers are distributed by being dispersed onto the substrate. When the spacers are dispersed, it is difficult to uniformly distribute the ball spacers on the substrate, and besides a precise cell gap cannot be maintained if the ball spacers are lumped. In addition, since the ball spacers themselves diffuse light which is transmitted through the liquid crystal layer, they result in deterioration of the image quality of the LCD device. To solve such a problem, the above-described column spacer is used. However, the column spacer 18 may cause the following problems.
Though not shown in FIG. 2, an alignment layer is applied to the first substrate 20 and the second substrate 30. The alignment layer has an alignment direction produced by a rubbing process. In the rubbing process, the alignment direction is determined by rubbing a rubbing roll having a rubbing cloth against the alignment layer to thereby form grooves on the alignment layer. Accordingly, a region where grooves are not formed by the rubbing is formed around the column spacer 18 which has almost the same height as the cell gap of the liquid crystal panel 1. In such a region, liquid crystal molecules are arranged in an irregular direction (i.e., alignment defective region) and light leakage occurs in a normally black mode.
Meanwhile, as shown in FIG. 1, when the common electrode 5 and the pixel electrode 7 are arranged at a certain angle with respect to a direction of the Y-axis and are symmetric in the pixel, the rubbing is performed along the direction of the Y-axis of the data line 4. Accordingly, when the column spacer 18 is arranged on the left side of the data line 4, a light leakage region in a band shape occurs on the left side of the data line 4 in the direction of the Y-axis, resulting in deterioration of an LCD display.